Glass containing lanthanum borosilicate and rich in aluminum oxide



March 23, 1965 GEFFCKEN ETAL 3,174,871

GLASS I c LANTHAN BOROSILICATE AND RI IN ALUMIN OXIDE Filed July 27.1959 4 Sheets-Sheet 1 550 5o 5o Ila-806 0 "1om o Fig.7

La -O Si0 -B 0 10 A1 0 INVENTOPSI WALTER GEFFCKENMF/WHRGI? FA ULST/ hCKEN ETAL 3,174,871

G AINI ANTHANUM BOROS CATE March 23, 1965 GLASS RICH ALUMINUM OXID FiledJuly 27, 1959 4 Sheets-Sheet 2 $0 3O 4O 5O ;0 3 5 FFgZ la 0 -$:'O B 0 15Q1205 WALTH GEFFCKENJMAPM fluLT/CH ATTORNEYS Mam}! 1965 w. GEFFCKEN ETAL3, 7

GLASS CONTAINING LANTHANUM BOROSILICATE AND RICH IN ALUMINUM OXIDE FiledJuly 27, 1959 4 Sheets-Sheet 3 WALTER GEFFcKEN? Mme/x fiuLsTlcH f @W/ W*Y ATTORNEYS IN VE N TORS March 23, 1965 w. GEFFCKEN ETAL 3,174,871

GLASS CONTAINING LANTHANUM BOROSILICATE AND RICH IN ALUMINUM OXIDE FiledJuly 27, 1959 4 Sheets-Sheet 4 545552515049484246 /Qg.4$ z

INVENToRSI WALTER GEFFLKENQMMA FMILSTlCH X w W W L ATTORNEYS niteciStates The present invention relates to a glass composition containinglanthanum borosilicate and being rich in aluminum oxide.

There have been prior disclosures of glass compositions which have ahigh content of rare earths as well as aluminum oxide and silicic acid,and attain high 11., and v-values and a very good chemical stability.There have also been disclosures of glass compositions which, aside froma content of ThO and La O together amounting up to 45% by weight, acontent of at least 30% by weight of B and a content of 13 to 25% byweight in metals, preferably of the bivalent type, have an additionalcontent of A1 0 of up to 10% by weight. The refractive index of theseglass compositions was relatively low and in any case less than 1.70.

According to the present invention, it has now unexpectedly been foundthat in glass compositions which also contain boric acid and 7 to 21% byweight of aluminum oxide, the content of lanthanum oxide can be raisedto very high values of at least 50% by weight, and even up toapproximately 67% by weight, if these compositions have a content of atleast 7% by Weight of SiO and a content of boric acid of more than 6% byweight. It is then possible to attain very high n -values as well ashigh or even very high u-values, that is, a combination which is of thegreatest importance for the construction of optical systems.

Such glass compositions are in this respect far superior to the firstmentioned glass compositions of rare earths, A1 0 and SiO which do nothave any content of boric acid. On the other hand, they have the sameexcellent chemical stability as these compositions. Thus, for example,it is possible to produce stable glass compositions with an lt -value of1.794 and a v-va'lue of 47.

These new glass compositions are also more easily melted than thosewithout boric acid, since they require lower melting temperatures andare more easily refined.

The peculiar form of the stability range of the glass compositionsaccording to the invention will be illustrated in the accompanyingdrawings by means of a few threecomponent diagrams, in which FIGURE 1shows, in triangular coordinates, the threecomponent diagram of La O SiOand B 0 with a constant content of 10% by weight of A1 0 FIGURE 2 showsthe same with a content of 13% by weight of A1 0 FIGURE 3 shows the samewith a content of 16% by weight of Al O while FIGURE 4 shows in an n -vdiagram the optical position of a few examples of the new glasscompositions.

FIGURES l to 3 clearly indicate the steep ascent of the lanthanumcontent if more than 5% by weight of SiO are added, with the result thatat a content of A1 0 of to 13% by weight, the content of lanthanum oxidemay be increased to 56% by weight, and at a content of A1 0 of 16% byweight to 61% by weight, provided the compositions contain the minimumlimit in S10 of 7% by weight. The content in boric acid is then theresulting residue of 27 to 24% or 16% by weight, respectively.

It has further been found that the best possible optical position may,however, only be attained if the content in silicic acid will be furtherincreased. Thus, for example, at an A1 0 content of 10% by weight thecontent in Si0 amounts to approximately 12% by weight, at an A1 0content of 13% by weight it amounts to 11% by weight, and at an A1 0content of 16% by weight it amounts to 9% by weight. Consequently, thepercent age by weight of Si0 equals 16.5% by weight of Al O The lowerlimit of Si0 of 7% by Weight is attained according to the above formulawith an A1 0 content of 21% by weight. This value thus constitutes theupper limit of the A1 0 content of the glass compositions according tothe invention. Although stable and chemically resistant glasses may alsobe attained with higher A1 0 contents, the v-value will then be reducedso considerably that the expense involved by the high La O contents willbe too high in comparison to the advantages attained, and moreinexpensive materials together with lower A1 0 contents will thenusually be preferred.

The mentioned lower limit of B 0 of 6% by weight is indicated by thefact that at a reduction of the boric acid content to less than 6%,there will be a noticeable reduction in the receptivity for La OFurthermore, in the vicinity of 54% by weight of La O and B 0 contentsof 0 to 5% by weight there will be a strong inclination towardcrystallization, as may be seen by the shaded area in FIGURE 1. Thediagrams shown in FIGURES 1 to 3 indicate distinct maxima of the La Ocontent, especially with the Al O contents of 10 to 13% by weight. Itwas further found that, at a given n -value, the v-content will dropconsiderably if the boric acid content is lowered to a point below thelimit of 6% by weight.

If very high refractive indices are desired, as are attainable with thehighest La O contents of 65% by Weight and more, the boric acid contentshould be approximately equal to the silicic acid content.

If the refractive indices do not need to be quite as high, but theu-values with a given refraction should be as high as possible, thecomposition is preferably prepared so that, at a given refraction (thecurves for a constant refraction being indicated in the drawings), theboric acid content will be made as high as possible and as closely aspossible to the crystallization limit, as indicated. The boric acidcontent should therefore be in all these cases higher than the silicicacid content.

The upper limit of B 0 may be easily determined purely by calculation bydeducting the lower limits of the content in La o A1 0 and SiO from thetotal of 100 of all components. It then amounts to 36% by weight.Similarly, the upper limit of SiO will thus be determined by calculationas being 37% by weight.

The glass compositions according to the invention may thus be specifiedas follows:

Percent by weight L3203 t0 1160 7 to 21 i 2 7 to 37 B 0 6 to 36 in whichthe content of B 0 is then preferably made higher than that of SiO Veryremarkable optical positions may be attained with the glass compositionsaccording to the invention if the La O content is increased above byweight. In extreme glass types, the La O content should even exceed byweight.

At a content in 1.3203 of 55 or 60%, the respective limits of the SiOcontent lie, according to the above calculation, at 7 to 32% or 7 to 27%by weight, and the boric acid content at 6 to 31% or 6 to 26% by weight,respectively.

' tent of ZrO and Ta O Of course, certain quantities of other substancesmay also be added to the glass compositions according to the invention.Thus, for example, the La O may be partly replaced by CdO and/ or ZnOand/ or alkaline earths and/ or alkalies and/ or Pb() and/ or TiOHowever, at such a partial replacement by ZnO, alkaline earths, andalkalies, the residual La O content should not be less than 50% byweight, and at a replacement by CdO and PbO and TiO it should not beless than 45% and preferably not less than 50% by weight, while thesilicic acid content of a glass containing CdO or ZnO should preferablybe increased to at least 10% by weight since the crystallization limitis shifted in such glass compositions toward higher S10 contents.

In these new glass compositions it is also possible to replace a part ofthe A1 by amounts of up to by weight of ZrO Ta O W0 wherein the total ofthese components should not exceed by weight and the A1 0 content shouldnever be less than 7% by weight.

Since in glass compositions containing Ta O and ZrO the limit of thestable glass range is shifted toward smaller silicic acid contents, thecondition that the S10 content should be higher than 7% should thereforebe generally fulfilled by complying with the formula:

The influence of niobium is similar to that of tantalum. A part of theLa O may also be replaced by PbO. This results in glass compositionswith smaller v-values which lie within the range of the so-calledlanthanum flint-glass compositions. They may be very easily melted andrefined because of the simultaneous application in these compositions ofPbO and E 0 Also, because of the enlargernent of the glass rangerelative to otherwise similar The molten mixtures are thereafter stirreduntil they attain the viscosity necessary for casting; and they are castin the usual manner into preheated metallic molds and then cooled.

With reference to the 12 -11 diagram according to FIG- URE 4, it may beadded that the values indicated therein by squares correspond to theconventional glass com positions with the most extreme optical positionswhich are commercially obtainable, while the values indicated by dotscorrespond to the examples stated in Table I and those indicated bycircles to those stated in Table II.

Table l [Components in percent by weight] N0. LaQOZ A1203 S102 B203 71d11 63. 0 8. 0 13. 0 16. (l 1. 747 51. 0 60. 0 8.0 10. 0 p 22. 0 l. 73352. 3 60. 0 8. O 17.0 15. 0 1. 730 51'. 2 67. 0 10. 0 13.0 10.0 1. 77349. 3 65. 0 10. 0 15. 0 10. 0 l. 758 49. 9 65. O 10. 0 12. (l 13. 01.762 50. 2 GO. 0 10. 0 9. 0 21.0 1. 733 52. 0 60. 0 10. 0 12. 0 18.0 1. 733 51. 9 00. 0 10.0 23. 0 7. 0 1. 730 50. 9 55. 0 10. 0 20.0 15.0 1. 698 52. 6 07. 0 13.0 13. 0 7. 0 1. 778 48. 5 (15. 0 13. 0 12.0 10.0 1. 770 49. 0 (i0. 0 13. O 9. 0 .18; 0 1. 735 51. 0 60. 0 13. 0 18. O9. 0 1. 736 50. 6 54. 0 13.0 18. 0 15.0 1.705 52. 2 54.0 13.0 17.9 6.11.704 51.2 65. 0 16. 0 9. 0 10. 0 1. 766 48. 9 65. 0 16. 0 12. 9 6. 1 1.767 48. 5 60.0 16. 0 9. 0 l5. 0 1. 725 51. 8 55. 0 16. 0 9. 0 20. 0 1.707 52. 2 60. 0 20. 0 10. 0 10. 0 1. 736 50. 2 60. 0 20. 0 13. 9 G. l l.736 50. 0

Table 11 [Components in percent by weight] glass compositions which arefree of boric acid, it is possible to produce glass compositions with avery high M203 M203 S102 B203 refractive index. By changing the ratio oflanthanum 0 130cm 1 755 47 8 oxide to PhD, the v-values may be veryeasily adjusted to 268 [$8 12:8 [8;8 5 j: 1:746 1 any part1cular valuewrthln very wide limits. The same 63-8 12-8 2-8 3-8 2 8 applies toadditions of TiO however, the amount there- 2 i 1 gj '5 11766 of addedshould not exceed 5% by weight smce a yellowg-g -8 2-8 I 12% g g-8brownish discoloration would otherwise occur. [2 8 0 0 5 145 1 Theaccompanymg tables show a compilation of nu- 23-8 138 13-8 9-8 38 gmerous examples of the glass compositions according to 1 1 1:768 1 th iti 5?. 0 13. 0 5. 0 2;). 0 5.0 a :3. lfor producing the new glasscompositions, the raw ma- 2818 i218 5:8 318 218 722 terials should beapplied in as pure a cond1t1on as possible, 5110 13. 0 0 0 711 and La OSiO CdO, ZnO, W0 ZrO and Ta O are T able III [Components in percent byweight] No. 1121403 A110 S10 B 0 B210 ZIOz PbO T102 Ta O m y preferablyapplied in the form of oxides, while A1 0 is applied in the form of ahydrated oxide, and E 0 in the form of boric acid hydrate. Thesematerials should be intimately mixed and melted, preferably in aplatinum crucible, at temperatures of 1300 to 1500 C.

The lowest temperature applies to the composition No. 7 in Table I witha content in SiO +Al O of only 19% and 21 B 0 content of 21%. Thehighest temperatures are required for the compositions with a content inZrO and Ta205. I p

The refining temperature preferably lies between 1360 and 1550 C.Naturally, the highest refining temperatures are also required for theglass compositions with a con- Generally, however, a refiningtemperature of 1400 to 1420 will be sufiicient.

Although our invention has been illustrated. and described withreference to the preferred embodiments thereof, we wish to have itunderstood that it is in no way limited to the details ofsuchembodiments, but is capable of numerous modifications Within thescope of the appended claims; 7

Having thus fully disclosed our invention, what we claim is:

1. A lanthanum borosilicate glass containing aluminum oxide and havingan n value of from about 1.67-1.80 :and a 11 value of from about 40-55consisting of 67% by weight of La O 721% by weight of Al O 7-37% byweight of S10 and 636% by weight of B 0 2. A giass as claimed in claim 1having an n value of from about 1.70-1.80 and a 1/ value of from about 540-53 consisting of 55-67% by weight of La- O 7-21% by weight of A1 07-32% by weight of SiO and 631% by weight of B 0 3. A glass as claimedin claim 1 having an n value of from about 1.72-1.80 and a 1 value offrom about 40-525 consisting of 60-67% by weight of La O 7-21% by weightof A1 0 7-27% by weight of SiO and 6-26% by Weight of B 0 4. A glass asclaimed in claim 1 in which B 0 is present in an amount greater thanone-half the sum of the total of B 0 and SiO present in said glass.

5. A glass as claimed in claim 3 in which the SiO 6 is present in anamount equal to 16 minus 45% of said A1 0 present.

6. A lanthanum borosilicate glass containing aluminum oxide and havingan n value of from about 1.67-1.80 and a 11 value of from about 40-53consisting of 50-67% by weight of La O 721% by weight of A1 0 7-37% byweight of SiO and 6-36% by weight of B 0 References Cited in the file ofthis patent UNITED STATES PATENTS

1. A LANTHANUM BOROSILICATE GLASS CONTAINING ALUMINUM OXIDE AND HAVINGAN ND VALUE OF FROM ABOUT 1,67-1.80